Many types of conventional semiconductor device are composed of a semiconductor die mounted in a packaging device. One type of packaging device widely used in the industry includes a metal lead frame. A metallization layer of aluminum located on the bottom surface of the semiconductor die is bonded to a conductive surface that forms part of the lead frame to attach and electrically connect the die to the lead frame. Additionally, electrical connections are made between bonding pads on the top surface of the die and other leads of the lead frame to provide additional electrical connections to the die. The lead frame and semiconductor die are then encapsulated to complete the semiconductor device. The packaging device protects the semiconductor die and provides electrical and mechanical connections to the die that are compatible with conventional printed circuit board assembly processes.
In such conventional semiconductor devices, the bottom surface of the die is typically bonded to the conductive surface of the lead frame using a silver epoxy adhesive that cures at a relatively low temperature, typically about 120° C. The curing temperature of the silver epoxy adhesive is compatible with the other materials of the packaging device.
The volume of the packaging device used in such conventional semiconductor devices, i.e., the lead frame and the encapsulant, is typically many times that of the semiconductor die. This makes such conventional semiconductor devices unsuitable for use in applications in which a high packing density is required. A high packing density allows miniaturization and other benefits. Therefore, what is needed is a semiconductor packaging device that is comparable in volume with the semiconductor die and that is compatible with conventional printed circuit board assembly processes.
Recently, semiconductor die having a substrate surface metallization layer of a gold-tin alloy (80% Au:20% Sn approximately) have been introduced in light-emitting devices. Such semiconductor die typically have a substrate of sapphire, silicon carbide or a Group III-V semiconductor material, such as gallium arsenide. Semiconductor devices having substrates of the first two substrate materials have layers of Group III-V semiconductor materials, such as gallium nitride, deposited on their substrates. The die attach process for such semiconductor die uses a gold-tin eutectic, which has a melting point of about 280° C. Temperatures as high as about 350° C. can be encountered in the die attach process for such die. Such high temperatures are incompatible with the materials of many conventional packaging devices. Thus, what is also needed is a packaging device for semiconductor die that use a high-temperature die attach process.
Many printed circuit assembly processes and assembly equipment require the use of standard semiconductor device packages. Modifying such processes to use a new semiconductor device package can be expensive and can interrupt production. Therefore, what is additionally needed is a way to mount a semiconductor die that requires a high-temperature die attach process in a conventional packaging device.